c#摄像头拍照

using System;
using System.Runtime.InteropServices;
using System.Drawing;
using System.Drawing.Imaging;

namespace Video
{
/// <summary>
/// 一个控制摄像头的类
/// </summary>
public class VideoWork
{
private const int WM_USER = 0x400;
private const int WS_CHILD = 0x40000000;
private const int WS_VISIBLE = 0x10000000;
private const int WM_CAP_START = WM_USER;
private const int WM_CAP_STOP = WM_CAP_START + 68;
private const int WM_CAP_DRIVER_CONNECT = WM_CAP_START + 10;
private const int WM_CAP_DRIVER_DISCONNECT = WM_CAP_START + 11;
private const int WM_CAP_SAVEDIB = WM_CAP_START + 25;
private const int WM_CAP_GRAB_FRAME = WM_CAP_START + 60;
private const int WM_CAP_SEQUENCE = WM_CAP_START + 62;
private const int WM_CAP_FILE_SET_CAPTURE_FILEA = WM_CAP_START + 20;
private const int WM_CAP_SEQUENCE_NOFILE =WM_CAP_START+ 63;
private const int WM_CAP_SET_OVERLAY =WM_CAP_START+ 51;
private const int WM_CAP_SET_PREVIEW =WM_CAP_START+ 50;
private const int WM_CAP_SET_CALLBACK_VIDEOSTREAM = WM_CAP_START +6;
private const int WM_CAP_SET_CALLBACK_ERROR=WM_CAP_START +2;
private const int WM_CAP_SET_CALLBACK_STATUSA= WM_CAP_START +3;
private const int WM_CAP_SET_CALLBACK_FRAME= WM_CAP_START +5;
private const int WM_CAP_SET_SCALE=WM_CAP_START+ 53;
private const int WM_CAP_SET_PREVIEWRATE=WM_CAP_START+ 52;
private IntPtr hWndC;
private bool bWorkStart = false;
private IntPtr mControlPtr;
private int mWidth;
private int mHeight;
private int mLeft;
private int mTop;

/// <summary>
/// 初始化显示图像
/// </summary>
/// <param name="handle">控件的句柄</param>
/// <param name="left">开始显示的左边距</param>
/// <param name="top">开始显示的上边距</param>
/// <param name="width">要显示的宽度</param>
/// <param name="height">要显示的长度</param>
public VideoWork(IntPtr handle, int left, int top, int width,int height)
{
mControlPtr = handle;
mWidth = width;
mHeight = height;
mLeft = left;
mTop = top;
}

[DllImport("avicap32.dll")]
private static extern IntPtr capCreateCaptureWindowA(byte[] lpszWindowName, int dwStyle, int x, int y, int nWidth, int nHeight, IntPtr hWndParent, int nID);

[DllImport("avicap32.dll")]
private static extern int capGetVideoFormat(IntPtr hWnd, IntPtr psVideoFormat, int wSize );
[DllImport("User32.dll")]
private static extern bool SendMessage(IntPtr hWnd, int wMsg, int wParam, long lParam);

/// <summary>
/// 开始显示图像
/// </summary>
public void Start()
{
if (bWorkStart)
return;

bWorkStart = true;
byte[] lpszName = new byte[100];

hWndC = capCreateCaptureWindowA(lpszName,WS_CHILD|WS_VISIBLE ,mLeft,mTop,mWidth,mHeight,mControlPtr,0);

if (hWndC.ToInt32() != 0)
{
SendMessage(hWndC, WM_CAP_SET_CALLBACK_VIDEOSTREAM, 0, 0);
SendMessage(hWndC, WM_CAP_SET_CALLBACK_ERROR, 0, 0);
SendMessage(hWndC, WM_CAP_SET_CALLBACK_STATUSA, 0, 0);
SendMessage(hWndC, WM_CAP_DRIVER_CONNECT, 0, 0);
SendMessage(hWndC, WM_CAP_SET_SCALE, 1, 0);
SendMessage(hWndC, WM_CAP_SET_PREVIEWRATE, 66, 0);
SendMessage(hWndC, WM_CAP_SET_OVERLAY, 1, 0);
SendMessage(hWndC, WM_CAP_SET_PREVIEW, 1, 0);
//Global.log.Write("SendMessage");
}
return;

}
/// <summary>
/// 停止显示
/// </summary>
public void Stop()
{
SendMessage(hWndC, WM_CAP_DRIVER_DISCONNECT, 0, 0);
bWorkStart = false;
}

/// <summary>
/// 抓图
/// </summary>
/// <param name="path">要保存bmp文件的路径</param>
public void GrabImage(string path)
{
IntPtr hBmp = Marshal.StringToHGlobalAnsi(path);
SendMessage(hWndC,WM_CAP_SAVEDIB,0,hBmp.ToInt64());
}
}
}

 

这是一个控制摄像头进行拍照的类，我每次使用GrabImage抓图都是225K的一张照片，我想请问如何才能让我抓到的图片小一些，我想控制在70K左右。不知怎么让拍照的像素变小？

 

if(this.Request.QueryString["filename"]!=null)
{
                //获取原图片
string filename=this.Request.QueryString["filename"];
Bitmap bmpOld=new Bitmap(this.Server.MapPath("images/" + filename));
    //计算缩小比例
double d1;
if(bmpOld.Height>bmpOld.Width)
d1=(double)(MaxLength/(double)bmpOld.Width);
else
d1=(double)(MaxLength/(double)bmpOld.Height);
//产生缩图
Bitmap bmpThumb=new Bitmap(bmpOld,(int)(bmpOld.Width*d1),(int)(bmpOld.Height*d1));
//清除缓冲
Response.Clear();
//生成图片
bmpThumb.Save(this.Response.OutputStream,ImageFormat.Jpeg);
Response.End();
//释放资源
bmpThumb.Dispose();
bmpOld.Dispose();
}